Cold Start Period Research Articles

Toward gasoline vehicles with zero harmful emissions by storing NO at Pd nanoparticle–CeO2 interface during the cold-start period

A significant amount of NO is emitted from advanced gasoline vehicles during preheating three-way catalysts (TWCs) to operating temperature (>150°C). Pd nanoparticles (NPs) loaded on CeO2 are studied as a NO abatement material to mitigate NO emissions during the cold-start period. The air-fuel equivalence ratio is systematically switched from high to low while increasing temperature to promote NO storage below the operating temperature of TWCs and NO reduction at high temperature. Combined experimental and theoretical studies indicate that the Pd-NP–CeO2 interface modified by oxygen vacancies (VOs) plays an important role in converting NO∗ to NO2. NO2 is captured by VOs formed on the CeO2 surface, enabling the use of Pd/CeO2 as a NO storage material. Consequently, NO emission decreases by 67.6% during the cold-start period under practical conditions, which has been unattainable with conventional TWCs, thus bringing us a step closer to zero harmful emissions.

An Analysis of Emissions from An Ethanol Flex-Fuel Vehicle under Two Distinct Driving Cycle Tests during Cold Start

Ethanol flex-fuel vehicles are introduced to Thailand’s market and believed that they provide an alternative way in terms of reducing crude oil and octane booster import. Many literatures suggested that they also helped to reduce some emission species including the greenhouse gas. However, sufficient proof of this flex-fuel vehicle comparing the conventional versus realistic driving cycle tests during cold starts is not clearly identified. This research focuses on the comparison of performance, fuel consumption, and emissions of a flex-fuel vehicle using Gasohol E10, E50, and E85 tested under the New European Driving Cycle (NEDC) and Bangkok Driving Cycle (BDC). Tests were done on a Chassis Dynamometer in the Automotive Emission Laboratory of the Pollution Control Department. Considering emission data from both test cycles, the more ethanol ratios in gasoline, the more CO, NMHC, NOx, CO2 and PN emissions reductions. On the contrary, HC emissions are increased but still under EURO4 standards. Fuel consumptions on E85 are increased around 30% compared to E10 for both test cycles. However, the pattern of driving cycles significantly impacts the amounts of CO/NOx emissions and fuel consumption. During cold start periods, regardless of percentages of ethanol blends, the amounts of HC and CO emissions for both test cycles are similar due to running engine in rich conditions by ECU management to warm three-way catalyst. On the contrary, NOx emissions are strongly related to frequent acceleration and deceleration sequences of the tested driving cycle.

Insight into CO induced degradation mode of Pd/SSZ-13 in NOx adsorption and release: Experiment and modeling

Passive NOx adsorption (PNA) on Pd zeolites is an important technique to remove NOx during the cold start of the engine. However, the stability of Pd zeolites under high concentrations of CO is still challenging in multiple cold starts of an engine. Herein, we illustrate the CO-induced degradation mechanism of Pd zeolite by combining experiments and kinetic models. Pd/SSZ-13 has been used in multicycle processes containing NOx adsorption at low temperature and temperature programmed desorption, which represents the PNA degradation in multiple cold start periods. A kinetic model was developed to describe the NOx storage and degradation behavior of Pd/SSZ-13. Both experimental and modelling observations suggested that two Pd sintering modes are occurring under high CO concentration (4000 ppm), namely Ostwald ripening and particle migration. Apart from the degradation behavior, this model is also adequate for describing multi-cycle NOx storage and release behavior under low CO concentration.

Direct incorporating small amount of Ce (III) in Cu-SAPO-18 catalysts for enhanced low-temperature NH3-SCR activity: Influence on Cu distribution and Si coordination

The reduction of NOx emission during the cold start period of diesel vehicles requires special attention in accordance with the emission regulations. In this work, the direct incorporation of cerium and copper in SAPO-18 catalyst with AEI type framework structure (CuCe-SAPO-18) resulting in a substantial enhancement of the performance in the low-temperature NH3-SCR reaction (<200 ℃). A small amount of cerium (0.13–0.31 wt%) broadened the reaction temperature range of use and increased the hydrothermal stability of the catalyst considerably. The cerium species was introduced in the ion-exchange sites of Cu-SAPO-18 in the form of Ce3+ ions even with high loading (3.15 wt%). The Ce3+ ions were found to affect the distribution of silicon and aluminum atom coordination (29Si NMR, 27Al MAS NMR) in the AEI-type skeleton structure leading to an increase of both the amount of active Cu2+ species and the acidity of the CuCe-SAPO-18 catalysts that are beneficial for the NH3-SCR reaction.

Particulate number emissions during cold-start with diesel and biofuels: A special focus on particle size distribution

The share of biofuels in the transportation sector is increasing. Previous studies revealed that the use of biofuels decreases the size of particles (which is linked to an increase in particulate toxicity). Current emission regulations do not consider small particles (sub-23 nm); however, there is a focus in future emissions regulations on small particles. These and the fact that within cold-start emissions are higher than during the warmed-up operation highlight the importance of a research that studies particulate matter emissions during cold-start. This research investigates the influence of biofuel on PN and PM concentration, size distribution, median diameter and cumulative share at different size ranges (including sub-23 nm and nucleation mode) during cold-start and warm-up operations using diesel and 10, 15 and 20% mixture (coconut biofuel blended with diesel). During cold-start, between 19 and 29% of total PN and less than 0.8% of total PM were related to the nucleation mode (sub-50 nm). Out of that, the share of sub-23 nm was up to 9% for PN while less than 0.02% for PM. By using biofuel, PN increased between 27 and 57% at cold-start; while, the increase was between 4 and 19% during hot-operation. The median diameter also decreased at cold-start and the nucleation mode particles (including sub-23 nm particles) significantly increased. This is an important observation because using biofuel can have a more adverse impact within cold-start period which is inevitable in most vehicles’ daily driving schedules.

ОПРЕДЕЛЕНИЕ ОПТИМАЛЬНОЙ ТЕМПЕРАТУРЫ МОТОРНОГО МАСЛА, ПРИ КОТОРОЙ ВОЗМОЖЕН ЗАПУСК ДВИГАТЕЛЯ С МИНИМАЛЬНЫМ ИЗНОСОМ

The operation of road transport implies not only the transportation of goods and passengers, but also the maintenance of the car itself. When operating road transport at low temperatures, the risk of failure of the main units increases. The most expensive unit is the internal combustion engine, which experiences a tremendous load during the cold start period. This load depends on the viscosity of the engine oil, which, in turn, is directly dependent on temperature. The greatest danger from the point of view of engine operation without lubrication is the period of engine operation after start-up. In order to increase the viscosity of the oil, improve the starting quality of the engine and reduce starting wear, it is necessary to use engine preheating. The purpose of this work is to identify the temperature or temperature range at which it is possible to “safely” start the engine with pre-start preparation at low temperatures. The temperature range depends on the operating conditions of the vehicles, the methods of pre-start preparation of the engine, which in turn affects the time of pre-start preparation. The paper reveals the temperature range for starting an internal combustion engine at low temperatures with the least wear of rubbing parts and minimal pre-launch costs; the recommended engine oil temperatures before starting internal combustion engines are given.

EGR cylinder deactivation strategy to accelerate the warm-up and restart processes in a Diesel engine operating at cold conditions

The aftertreatment systems used in internal combustion engines need high temperatures for reaching its maximum efficiency. By this reason, during the engine cold start period or engine restart operation, excessive pollutant emissions levels are emitted to the atmosphere. This paper evaluates the impact of using a new cylinder deactivation strategy on a Euro 6 turbocharged diesel engine running under cold conditions (−7°C) with the aim of improving the engine warm-up process. This strategy is evaluated in two parts. First, an experimental study is performed at 20°C to analyze the effect of the cylinder deactivation strategy at steady-state and during an engine cold start at 1500 rpm and constant load. In particular, the pumping losses, pollutant emissions levels and engine thermal efficiency are analyzed. In the second part, the engine behavior is analyzed at steady-state and transient conditions under very low ambient temperatures (−7°C). In these conditions, the results show an increase of the exhaust temperatures of around 100°C, which allows to reduce the diesel oxidation catalyst light-off by 250 s besides of reducing the engine warm-up process in approximately 120 s. This allows to reduce the CO and HC emissions by 70% and 50%, respectively, at the end of the test.

Kinetic modeling of CO assisted passive NOx adsorption on Pd/SSZ-13

Passive NOx adsorption (PNA) has been recently developed as a promising technology for controlling the NOx emissions during the cold start period. In this work, we illustrate a CO-assisted mechanism by combining experimental and kinetic modeling studies. Pd/SSZ-13 has been synthesized, characterized and evaluated as a PNA in low-temperature NOx adsorption and temperature program desorption cycles, to represent multiple cold start periods. The gas compositions were also systemically changed, where both the effect of varying NOx and CO feed was evaluated in the presence of high water and oxygen contents. A kinetic model was developed to simulate the profiles of NO and NO2, including three initial Pd sites (Z-Pd(II)Z-, Z-[Pd(II)OH]+ and PdO). It is concluded from XPS and in situ DRIFTS experiments, flow reactor measurements and modelling observations that CO reduces Pd(II) species to Pd(I)/Pd(0) species, which increases the stability of the stored NOx species, resulting in a release above the urea dosing temperature. The model could well describe the experimental features, including the effect of CO. In addition, the model was used for full-scale catalytic converter simulations.

The performance improvement of direct injection engines in cold start conditions integrating with phase change material: Energy and exergy analysis

The cold start problem is still one of the most significant drawbacks of diesel engines, especially in cold climates despite all technological improvements of fuel injection and control systems. Starting diesel engines becomes more difficult at low ambient air and engine block temperatures. Moreover, the production of pollutant exhaust emissions increases during the cold start and warm-up period of the engine. In this study, the thermal energy storage system (TES) with phase change materials (PCMs) has been proposed to improve the cold start and warm-up performance and exhaust emission characteristics of diesel engines. The waste heat from the engine main coolant using as the heat source is transferred to TES with integrated PCM after the warm-up period of the engine for heat storage. Then, the latent and sensible heat stored in PCM is transferred to the engine manifold to increase the temperature of intake air during cold start. The experiments have been conducted under low dead state temperature (≈6 ⁰C) conditions of the engine block and ambient. The experimental and energy-exergy comparison analysis results show that the cold start cranking period, CO and HC exhaust emission performances have improved by approximately 68.2%, 27.5% and 44% compared to classical engine system with the use of a designed TES, respectively. The efficiency of the strategy of increasing the intake air temperature by designing a PCM-based TES is supported by energy and exergy comparison analysis. Thermal efficiency and exergy efficiency improved in the range of 1.02%-7.45% and 0.9%-9.63%, respectively. These improvements show that the performance of a diesel engine under cold start conditions can be improved with a PCM-supported TES system.

Experimental validation for enhancement of PEMFC cold start performance: Based on the optimization of micro porous layer

The cold start is one of the key research fields in PEMFC studies. The improvement of PEMFC’s (proton exchange membrane fuel cell) unassisted cold start performance has played a positive role in promoting the industrialization and commercialization of FCV (fuel cell vehicle). In this work, as the key point of MEA (membrane electrode assembly) structure optimization, MPL (micro porous layer) aims to make the generated water can be retained in the CLs (catalyst layer) and membrane in the form of membrane water at the initial period of cold start. And the cold start performance of the optimized MEA single cell and stack are observed and analyzed by the segmented cell technology. After comparing with the cold start performance of the commercial MEA single cell and stack under the same conditions, the improvement of the cold start performance is verified. The single cell of MEA1 could achieve a quick unassisted cold start at a start-up temperature of −15 °C, and the cold start time under 0.2 V in CV (constant voltage) mode is 153 s, while the commercial MEA single cell can only achieve a successful cold start under the minimum start-up temperature of −10 °C. The optimized MEA stack can realize a quick unassisted cold start at a startup temperature of −20 °C, and the cold start time under 0.1 V in CV mode is 63 s, while the commercial MEA stack can only achieve a successful cold start under the minimum startup temperature of −15 °C.

Cold-start performance investigation of fuel cell electric vehicles with heat pump-assisted thermal management systems

In this study, the cold-start performance of fuel cell (FC) electric vehicles was investigated via integration of a heat pump system with a thermal management system (TMS). A model for the proposed heat pump-assisted TMS and FC stack was developed using experimental data. On the basis of the validated model, the potential of the heat pump-assisted TMS was comprehensively evaluated from the standpoint of three critical factors: air velocity, compressor speed, and coolant volume flow rate (VFR). Consequently, it was observed that the cold-start performance can be maximized in the case of a large coolant VFR, high compressor speed, and air velocity above 0.96 m s−1. Among the three variables, the most dominant was the coolant VFR, followed by the air velocity. When the compressor speed, air velocity, and coolant VFR were optimized, the cold-start time and total energy consumption of the heat pump-assisted TMS could be reduced by 29.9 and 11.3%, respectively, when compared to those of the baseline TMS during the cold-start period. In addition, an increase in the ambient temperature improved cold-start performance with the heat pump-assisted TMS.

Analysis of real-driving emissions from light-duty gasoline vehicles: A comparison of different evaluation methods with considering cold-start emissions

Cold-start emissions from road vehicles are an important source of air pollution. However, how to evaluate them in the real driving emission (RDE) test is controversial. Although the Commission Regulation (EU) 2017/1154 and 2018/1832 successively adopt the moving averaging window (MAW) method and the cumulative averaging (CA) method to calculate the emission factors that include the cold-start emissions in the RDE tests, both the methods have been found to be flawed when processing the RDE data including cold-starts. To demonstrate the problem, the RDE test data from three light-duty gasoline vehicles were comparatively analyzed using the MAW method and the CA method. Results reveal that the MAW method unreasonably underestimates cold-start emissions in the urban and total trip emission evaluation, and the CA method tends to increase the inconsistency of the RDE evaluation results. Considering the inherently different characteristics between the cold-start emissions and the non-cold-start emissions, this paper proposes that the entire RDE test trip should be divided into a cold-start trip and a non-cold-start trip, and the cold-start emissions are evaluated by the CA method while the non-cold-start emissions are evaluated by the MAW method. Furthermore, the pollutant emission factors in the cold-start trip are corrected referring to the CO2 emissions emitted during the cold-start period of Worldwide harmonized Light vehicles Test Cycle (WLTC). Using this proposed approach, the aforementioned RDE tests were further analyzed and evaluated again. It is verified that the consistency of the test evaluation results in the RDE tests can be improved. The results of this study could be used to improve future emission regulations for the more reasonable evaluation of cold-start emissions in RDE tests.

Local structure and NO adsorption/desorption property of Pd2+ cations at different paired Al sites in CHA zeolite.

Recently, Pd-exchanged CHA zeolites (Pd-CHA) have attracted attention as promising passive NOx adsorbers (PNAs) for reducing NOx emissions during the cold start period of a vehicle engine. In this work, the relationship between the local structures and the NO adsorption/desorption properties of the Pd cations in CHA zeolites was investigated. Pd cation formation and NO adsorption were theoretically explored by density functional theory (DFT) calculations for different paired Al sites in six-/eight-membered rings (6MR/8MR). Furthermore, we prepared a series of Pd-CHAs with different Pd loadings (0.5-5.4 wt%) and evaluated their NO adsorption/desorption properties by in situ infrared (IR) spectroscopy and temperature-programmed desorption (TPD) measurements. The increase in the Pd loading resulted in a shift in the NO desorption temperature toward a higher temperature regime. This phenomenon was ascribed to the increase in the proportion of less stable Pd cations, resulting in improved NO adsorption. Furthermore, the effect of Al distribution on the NO adsorption property of Pd-CHA was examined using CHA zeolites containing different proportions of paired Al sites in 6MR while maintaining similar Si/Al ratios (Si/Al = 12.0-16.5). The present study, based on a combination of theoretical and experimental techniques, shows that the NO adsorption/desorption properties over Pd-CHA can be tuned by controlling the Pd loading amount and the type of paired Al sites.

The effect of after-treatment techniques on the correlations between driving behaviours and NO emissions of passenger cars

Nitrogen oxides (NO x ) emissions from passenger cars are significantly dependent on after-treatment techniques, cold start conditions, and driving behaviours. The widely-used selective catalytic reduction (SCR) technique has low effectiveness of reducing NO x emissions during the cold start period or at low speeds. As a new technique, ammonia creation and conversion technology (ACCT) system can further decrease NO x emissions to achieve cleaner travelling. The correlations between driving behaviours and NO x emissions are different for vehicles equipped with SCR and ACCT systems over cold start and warm start driving cycles. In this paper, the effect of SCR and ACCT systems on the correlations between driving behaviours and NO x emissions were explored based on worldwide harmonized light vehicle test cycles (WLTC). The results indicated that vehicle fuel consumption rates almost linearly increased with acceleration when the acceleration was higher than −0.5 m/s 2 . For cold start situations, vehicle speed range of 55 km/h∼ 100 km/h presented the lowest NO x emission factors over SCR and ACCT scenarios. SCR efficiency was lower than 60% for the vehicle speed range of 25 km/h∼ 40 km/h, and the efficiency of ACCT system was higher than 65% in the corresponding speed range. Regarding the warm start scenarios, average catalyst efficiency was higher than 80% for SCR system over the speed range of 25 km/h∼ 40 km/h, and ACCT efficiency was higher than 95% for all the speed and acceleration ranges. Applications of ACCT systems provided a possibility of meeting stricter emission regulations, and the relationships between driving behaviours and NO x emissions provided the guidance for eco-driving to achieve cleaner travelling. • Effect of NO x reduction techniques on correlations of NO x and driving behaviours. • Catalyst efficiency was <50% for part of medium-low engine speed after warm up. • SCR efficiency was <60% in the speed range of 30 km/h∼ 40 km/h over cold start case. • Speed range of 30–60 km/h dominated total pipe-out NO x emissions for all the cases. • Pipe-out NO x emission factors were less depended on vehicle acceleration than speed.

Effects of ambient temperature and cold starts on excess NOx emissions in a gasoline direct injection vehicle

Studies have demonstrated that vehicles with gasoline direct injection (GDI) engines produce significantly higher emissions during a cold start than under hot-stabilized periods. A cold start is typically defined by the temperature of the engine or the catalytic converter; its extended effect on emissions, after the vehicle reaches the warm-up stage, has seldom been investigated. In this study, the influence of the post cold start period on nitrogen oxides (NOx) emissions was evaluated using real-world measurements. Vehicle on-board diagnostic data, fuel consumption, and emissions of multiple pollutants were collected on a 2020 GDI sports utility vehicle equipped with a Portable Emission Measurement System (PEMS). A total of 31 trips, with two drives per day, were conducted along arterial roads and highways in Toronto, Canada. The results indicate that during the first trip of the day after an overnight soak, the average NOx emission rate was 0.27 g/litre and 0.037 g/km, 384% and 299% higher than the emission rate on the second trip of the day. The amount of trip total NOx emissions is positively associated with the length of the catalytic converter warm-up period with correlation coefficient 0.67. We also observe that the catalyst warm-up time is negatively correlated with ambient temperature, and a negative relationship between ambient temperature and NOx emissions throughout the trip is depicted with correlation coefficient −0.44. The measured data reveal an extended effect of the cold start on NOx emissions even after the temperatures of the engine coolant and catalyst reach a stable level.

Recent advances in catalytic automotive emission control: Passive NO storage at low temperatures

AbstractIn the practical applications, a high portion of the NOx is emitted without purification in the cold start period of engine because the selective catalytic reduction (SCR) or NOx storage and reduction (NSR) catalysts are not warmed up. Passive NOx absorbers (PNA) were proposed earlier to store the NOx at low temperatures and release the stored NOx during warm‐up period when the SCR and NSR catalysts downstream are functional, while this concept just attracted great interests recently to meet the extra stringent requirement of governmental emissions regulations. A plant of PNA catalysts, showing different NO adsorption/release characteristics, was disclosed. This review summarizes the recent progress in the development of PNA catalysts. The characteristics of NO adsorption/release on precious metal (i.e., Pt, Pd) loading Al2O3 support catalysts, CeO2 support catalysts, and zeolite support catalysts are summarized and compared.

Combustion Analysis of a Diesel Engine during Warm up at Different Coolant and Lubricating Oil Temperatures

A comprehensive analysis of combustion behaviour during cold, intermediately cold, warm and hot start stages of a diesel engine are presented. Experiments were conducted at 1500 rpm and 2000 rpm, and the discretisation of engine warm up into stages was facilitated by designing a custom drive cycle. Advanced injection timing, observed during the cold start period, led to longer ignition delay, shorter combustion duration, higher peak pressure and a higher peak apparent heat release rate (AHRR). The peak pressure was ~30% and 20% and the AHRR was ~2 to 5% and ±1% higher at 1500 rpm and 2000 rpm, respectively, during cold start, compared to the intermediate cold start. A retarded injection strategy during the intermediate cold start phase led to shorter ignition delay, longer combustion duration, lower peak pressure and lower peak AHRR. At 2000 rpm, an exceptional combustion behaviour led to a ~27% reduction in the AHRR at 25% load. Longer ignition delays and shorter combustion durations at 25% load were observed during the intermediately cold, warm and hot start segments. The mass fraction burned (MFB) was calculated using a single zone combustion model to analyse combustion parameters such as crank angle (CA) at 50% MFB, AHRR@CA50 and CA duration for 10–90% MFB.

Temperature Effects in Polymer Electrolyte Membrane Fuel Cells

AbstractThe behavior of proton exchange membrane fuel cells (PEMFCs) strongly depends on the operational temperatures. In mobile applications, for instance in fuel cell electric vehicles, PEMFC stacks are often subjected to temperatures as low as −20 °C, especially during cold start periods, and to temperatures up to 120 °C during regular operation. Therefore, it is important to understand the impact of temperature on the performance and degradation of hydrogen fuel cells to ensure a stable system operation. To get a comprehensive understanding of the temperature effects in PEMFCs, this manuscript addresses and summarizes in‐ situ and ex‐ situ investigations of fuel cells operated at different temperatures. Initially, different measurement techniques for thermal monitoring are presented. Afterwards, the temperature effects related to the degradation and performance of main membrane electrode assembly components, namely gas diffusion layers, proton exchange membranes and catalyst layers, are analyzed.

Cold start emissions from a gasoline engine in RDE tests at different ambient temperatures

The implementation of the 3rd package of the RDE test procedure has extended the test method by considering emissions from a cold start period into the total exhaust emissions from a vehicle. The article presents the research results of exhaust emissions of a vehicle equipped with a gasoline engine. The tests were carried out at two different ambient temperatures, in line with the requirements of the RDE test procedure for passenger cars, meeting the Euro 6d-Temp emissions standard. The obtained results were analyzed, i.e. there were compared the engine and vehicle operating parameters and the values of road exhaust emissions during the cold start at two different ambient temperatures. The summary presents the shares of the cold start phase for each exhaust emission compound in the urban part of the test and the entire RDE test, depending on the ambient temperature (8ºC and 25ºC).

Testing and evaluation of cold-start emissions in a real driving emissions test

To properly evaluate the cold-start emissions of vehicles, four light-duty vehicles were selected to complete a Real Driving Emissions (RDE) test. The analysis and evaluation of the RDE test results reveal that the cold-start emissions account for a significant proportion of the urban trip emissions, and that the moving average window (MAW) method is not suitable for statistically processing the RDE test data that include the cold-start emission data. Additionally, three on-road emission tests including a cold-start test and two hot-start tests at different vehicle thermal states were designed to evaluate the effect of the initial vehicle thermal state on the vehicle start emissions. The results demonstrate that the thermal state of the TWC converter thermal state has a more direct and important effect on the cold-start emissions in the RDE test. Via a comparative analysis of the instantaneous characteristics of pollutant emission rates, fuel–air equivalent ratios, catalytic converter temperatures, vehicle trip dynamic parameters, etc., it is inferred that driving behavior has a more significant and sensitive impact on the cold-start emissions than on the non-cold-start emissions in the RDE test. Based on the RDE tests performed at different ambient temperatures, it is also indicated that the impact of the ambient temperature on the cold-start emissions is only a secondary factor relative to driving behavior. As a result, the trip dynamic conditions, specifically those for the cold-start period, should be set more reasonably and effectively in future RDE regulations to ensure the consistency of the cold-start emission test results.